Attacker Exploits Hyperbridge Vulnerability, Steals $250,000 in Polkadot Token Heist

Cryptocurrency hacks have become commonplace, but instances where attackers take significant risks only to reap minimal rewards are rare. Such a scenario unfolded on Sunday when an attacker exploited a vulnerability in Hyperbridge's cross-chain gateway.

This gateway connects different blockchains, enabling the attacker to mint 1 billion Polkadot tokens, valued at $1.19 billion, on the Ethereum network. The attacker then sold these tokens for approximately $237,000 in ether.

This exploit is the latest in a series of bridge vulnerabilities that have been exposed in 2026, including a $270 million Drift Protocol exploit on Solana last month. The Sunday attack targeted the bridge contract rather than Polkadot's core network, and the native DOT token remained unaffected. The vulnerability lay in how Hyperbridge's EthereumHost contract validated incoming cross-chain messages before passing them to the TokenGateway.

Bridges, which facilitate the transfer of coins between blockchains, are often the weakest link in cross-chain architecture. This is because they hold admin-level control over token contracts on destination chains, meaning a single validation failure can grant an attacker unlimited supply. The attack began when the attacker submitted a forged message via dispatchIncoming, which was then routed to TokenGateway.onAccept.

However, the request receipts check failed to verify the message against a valid cross-chain state commitment from Polkadot, instead storing an all-zeros commitment value. This suggested that the proof validation was either absent or circumventable for this specific call path, allowing the gateway to process the message as legitimate. The accepted message then executed changeAdmin on the bridged Polkadot token contract, transferring admin rights to the attacker's address.

With admin control, the attacker minted 1 billion tokens in a single transaction and routed them through Odos Router V3 into a Uniswap V4 DOT-ETH pool. The attacker extracted roughly 108.2 ETH across multiple swaps at slightly different prices.

The limited liquidity in the bridged DOT pool on Ethereum worked against the attacker, capping their profit. The pool's limited depth meant that the 1 billion tokens overwhelmed the available liquidity, resulting in the attacker receiving only a fraction of a cent per token. On a deeper pool or with a higher-value bridged asset, the same vulnerability would have led to significantly larger losses. As of Monday morning, DOT was trading just under $1.20.

CertiK flagged the exploit, confirming that the attack vector was the Hyperbridge gateway contract and that the attacker profited approximately $237,000 from minting and selling the bridged tokens. Hyperbridge has not publicly commented on the exploit or disclosed whether other bridged token contracts using the same gateway are vulnerable to the same forged-message attack vector.